Well 300nm is up in the ultra violet region. Can you get 300nm detectors?You would have to look at the sensitivity curve in the data sheet but in general a high energy photon will always induce current in a low energy photon detector without filtering.

Practically speaking, the farther off the wavelength is off from the tuned receiver, the less it will respond. This is how the eye works with just being able to see only 3 colours, red, green and blue. All three receivers have some overlap (the red receiver overlaps green, but red doesn't overlap blue that much). However, because of the different amount they respond to any wavelength, the brain can approximate what the wavelength is and attach a colour to that received radiation. See http://ed.ted.com/lessons/how-we-see-color-colm-kelleher.

What is it you are attempting to do? Does it have to be outside of the visible spectrum? Maybe you can stay within the same wavelength and use something like ALOHA protocol http://en.wikipedia.org/wiki/ALOHAnet. A close variant is used for Ethernet communication and all communication that uses a shared medium/band.

Or maybe you can try for different colour sensors?

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I want to use an IR transmitter that the receiver will not receive the transmitting IR signal or to receive the IR signal as little as possible.Should I use an 36Khz 940nm emitter or an 38Khz 880nm instead?

I want to use an IR transmitter that the receiver will not receive the transmitting IR signal or to receive the IR signal as little as possible.Should I use an 36Khz 940nm emitter or an 38Khz 880nm instead?

Preferable for the minimum efficiency of the my receiver is to use an emitter with different wavelength or different frequency?

I wasn't aware that emitters had a pulse frequency. I though only receivers did. Do you know what these numbers represent? The 'frequency' is the pulse rate (how many times it turns on and off), the 'wavelength' is what part of the electromagnetic spectrum it is using. I put these in quotes because a wavelength is the reciprocal of a frequency and vice versa.

If you are going to be using these (transmitting/receiving) at the same time and you don't want to get into protocol complications, you want to have each (the 'wavelength' and the 'frequency') as far off each other as is possible. This will reduce as much as possible crosstalk between the two.

AFAIK, emitters are just IR LEDs, you have to pulse them at the correct frequency. There are libraries available for this, but you'll have to look for them yourself.

Try here: http://lmgtfy.com/?q=arduino+ir+transmitter+library

If you have multiple receivers controlled by one chip, you may find that they may interfere with each other depending on how the library is implemented. Depending on your usage, you may be able to get away with one transmitter and one receiver per unit using a communication protocol like I stated earlier. If you don't require too much data going across these two channels, you might be able to get away with it by writing your own library.

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